Electric lamp



Sept. 18, 1962 R. G. LYE 3,054,921 ELECTRIC LAMP Filed Dec. 8, 1960 2 Sheets-Sheet 1 INVENTOR. R O B E R T G. LYE

B) Q ATTORNEJ/U N Sept. 18, 1962 R. G. LYE 3,054,921

ELECTRIC LAMP Filed Dec. 8, 1960 2 Sheets-Sheet 2 IN VEN TOR.

ROBERT G. LYE

' A T TORNEV United States Patent Ofi 3,054,921 Patented Sept. 18, 1962 ice 3,054,921 ELECTRIC LAMP Robert G. Lye, Cleveland, Ohio, assignor to Union Carbide Corporation, a corporation of New York Filed Dec. 8, 1960, Ser. No. 74,560 6 Claims. (Cl. 313112) The invention relates in general to electric lamps and refers more particularly to high pressure gas arc lamps.

High pressure gas are lamps are well-known as sources of intense light. These lamps generally comprise a pres sure container having a medium for transmitting light, two electrodes therein adapted to be energized by an electric current, and a gas therein which emits light upon excitation by energy supplied to it. Such lamps are used in street lights, motion picture projectors, and other devices which require intense illumination.

Due to mechanical problems concerning the lamps pressure container, however, commercially available high pressure inert gas are lamps are generally limited to two kilowatts of power. These mechanical problems exist in relation to the light transmitting medium of the pressure container. This medium, which in some cases is a window in an otherwise opaque pressure container and in other cases is the entire container, must be made of a transparent material that will withstand detrimental radiation and severe internal mechanical stresses.

At the present time, quartz is generally considered to be the best available material for the light transmitting medium of the pressure container, but it is not free of problems. For example, ultraviolet radiation degrades the optical characteristics of the quartz, and severe internal stresses in the quartz caused by thermal gradients and high pressures tend to produce devitrification of the quartz. Moreover, explosion hazards are proportional to the severity of the internal stresses.

Since inert gas are lamps are more efiicient at high pressures, a construction which makes possible the use of higher pressures is desirable. Such a construction should also make possible the reduction of thermal stresses present in the quartz and the reduction of ultraviolet radiation striking the quartz.

The primary object of the invention is, therefore, to provide a new and improved electric lamp which has longer operational life and higher power outputs.

Another object is to reduce optical degradation, the possibilities of devitrification, and the explosion hazards of an electric lamps pressure container.

In the accompanying drawing:

FIG. 1 is a vertical cross-sectional view of a high pressure gas are lamp embodying the invention;

FIG. 2 is a vertical cross-sectional View of a high pressure gas are lamp of somewhat different construction embodying the invention; and

FIG. 3 is a similar view of another form of high pressure gas are lamp embodying the invention.

The invention comprises a construction of a high pressure gas are lamp in which a transparent shield is interposed between the electrodes and the light transmitting medium of the pressure container. The shield is mounted so as to permit equalization of gas pressures on both faces of the shield and so as to parallel substantially the light transmitting medium of the pressure container.

In FIG. 1, the pressure container of the high pressure gas are lamp there illustrated comprises a water cooled cylinder with a water cooled plate 12 sealing one end and a circular quartz window 14 incorporated in a Water cooled annular attaching assembly 15 sealing the other end. All of these parts except the quartz window are suitably made of stainless steel. The quartz window 14 is the light transmitting medium of the pressure container,

and the void in the pressure container is filled with xenon.

A water cooled anode l6 and a water cooled cathode 18 enter the pressure container from opposite points on the cylinder 10, and are adapted to be energized by an external electric source (not shown). A packing gland 20 and a packing gland 22 seal the entrances of the anode 16 and the cathode 18.

A circular quartz shield 24 is removably interposed between the quartz window 14 and the anode 16 and cathode 18. Said quartz shield 24 substantially parallels said quartz window 14. Also, said quartz shield 24 is mounted with small openings 25 around its outer edge to permit equalization of gas pressures on both faces of said shield 24.

When the anode 16 and cathode 18 are energized by an electric current, an electric arc springs between the cathode 18 and anode 16. The xenon gas within the are is therefore in a state of high excitation, and said xenon emits intense white light as a result. The light escapes from the pressure container by passing through the quartz shield 24 and the quartz window 14.

The xenon becomes extremely hot during lamp operation. This creates thermal convection currents within the pressure container which, but for the shield 24, would transfer heat to the quartz window 14, creating thermal gradients and internal stresses therein.

Since lamp efliciency rises with increasing pressure of the xenon, the quartz window 14 must withstand severe internal pressure stresses for efiicient lamp operation as well as internal thermal stresses. The resultants of these two stresses produce severe mechanical loading of the quartz window 14, particularly near its exterior surface.

As indicated, the quartz shield 24 restricts the thermal convection currents which otherwise reach the quartz window 14 and thereby reduces the internal thermal stresses in said quartz window 14. This allows the lamp to operate at a higher pressure and efficiency or at a reduced mechanical loading in comparison with a similar lamp which does not have a quartz shield 24. Moreover, since explosion hazards are proportional to the severity of internal stresses, the explosion hazards may be reduced.

During lamp operation, the xenon and the electrodes in coaction emit harmful ultraviolet radiation as well as intense white light. The quartz shield 24 diminishes the amount of ultraviolet radiation which would otherwise be received by the quartz window 14. Since ultraviolet radiation degrades the optical characteristics of quartz, this reduces the rate of optical degradation of the quartz window 14. When the quartz shield 24 loses its optical efliciency as a result of the ultraviolet radiation, said shield 24 can be replaced.

In FIG. 2, the high pressure gas are lamp there shown has a spherical quartz envelope 26 as a pressure container and as a light transmitting medium. The anode 28 and the cathode 30 enter the quartz envelope 26 from opposite points on its surface, and are adapted to be energized by an external electric source (not shown). The void in the pressure container is filled with xenon, and gas tight seals 32 and 34 close the entrances of the anode 28 and cathode 30.

A quartz shield 36 is interposed between the spherical quartz envelope 26 and the anode 28 and cathode 30. The quartz shield 36 somewhat corresponds to the shape of the spherical quartz envelope 26 and substantially parallels said envelope 26. A circular break exists in the quartz shield 36, with an overlapping of the resulting edges, to permit equalization of gas pressures on both sides of said shield 36.

In FIG. 3, the high pressure gas are lamp there shown has a cylindrical quartz envelope 38 as a pressure container and as a light transmitting medium. The anode 40 and the cathode '42 enter the cylindrical quartz envelope 38 from opposite ends of the cylinder, and are adapted to be energized by an external electric source (not shown). The void in the pressure container is filled with xenon, and gas tight seals 44 and 46 close the entrances of the anode 40 and cathode 42.

A quartz shield 48 is interposed between the cylindrical quartz envelope 38 and the anode 4t and cathode 42. The quartz shield 48 somewhat corresponds to the shape of the cylindrical quartz envelope 38 and substantially parallels said envelope 38. One end of the cylindrical quartz shield 48 is open to allow equalization of gas pressures on both sides of said shield 48.

In both FIG. 2 and FIG. 3, the operation of the completed lamp is the same as described for FIG. 1, except that the quartz shields 36 and 48 are not replaceable.

Experiments were made with a high pressure gas arc lamp similar to FIG. 1 using xenon as the gas. After 110 hours of operation at a power average of 2.4 kilowatts, during which period power levels as high as 7 kilowatts were maintained, the shield was removed, and its optical transmittance was measured. The optical transmittance had decreased by 10 percent. The quartz window, however, showed no darkening or degradation in properties. The lamp has also been operated at power levels up to 11.5 kilowatts with no darkening or degradation of properties of the quartz window. The power limitation of 11.5 kilowatts was due to other incidental difficulties, not to the novel shield.

The invention is not limited to any one chemical composition of gas in the pressure container. Mixtures of gases may even be used to change the color characteristics of the light. Moreover, any transparent refractory material, such as quartz and natural or synthetic sapphire, can be used for the shield and/ or the light transmitting medium of the pressure container.

What is claimed is:

1. An electric lamp comprising a gas filled pressure container; a pair of electrodes mounted in said container and adapted to be electrically energized and when energized to produce light in coaction with said gas; a light transmitting medium in said container; and a shield made of a transparent material and interposed between said electrodes and said light transmitting medium; said shield being mounted so as to protect said light transmitting medium from detrimental radiation and thermal convection currents produced at said electrodes when said electrodes are energized and being mounted so as to permit equalization of gas pressures exerted on said shield; the gas pressures on each side of said shield being substantially equal at all times.

2. An electric lamp as defined in claim 1 wherein said shield is made of quartz.

3. An electric lamp as defined in claim 1 wherein said shield is removable and replaceable.

4. A high pressure gas arc lamp comprising a pressure container filled with a gas inert to chemical change; a pair of electrodes mounted in said container and adapted to be electrically energized and when energized to produce light in coaction with said gas; a light transmitting medium in said containers; and a shield made of a transparent material and interposed between said electrodes and said light transmitting medium; said shield being mounted so as to protect said light transmitting medium from detrimental radiation and thermal convection currents produced at said electrodes when said electrodes are energized and being mounted so as to permit equalization of gas pressures exerted on said shield; the gas pressures on each side of said shield being substantially equal at all times.

5. A high pressure gas are lamp as defined in claim 4 wherein said shield is made of quartz.

6. A high pressure gas are lamp as defined in claim 4 wherein said shield is removable and replaceable.

References Cited in the file of this patent UNITED STATES PATENTS 2,875,358 Rigden Feb. 24, 1959 2,919,369 Edgerton Dec. 29, 1959 2,982,877 Heine-Geldern May 2, 1961 

